As expected, Google has also released details on future pricing for App Engine.  Though the service will remain free for applications with less than 500 MB of storage requirements and 5 million page views per month, there will be a charge for applications exceeding the limit.  The expected fee structure announced by Google is very similar to that of Amazon Web Services:

Unlike Google App Engine, Amazon Web Services do not offer any type of free services but provides greater flexibility to developers.

You can sign up for Google App Engine account to start building and deploying applications.

What Does It Offer

• A fully featured integrated development environment
• Scalability and Reliability like Google’s own services
• Easy integration with Google’s services
• Dynamic resource allocation for ease of deployment

What Does It Include

The Google Apps Engine is comprehensive and fully equipped to create, deploy and run web applications.  Here are the various components which make up the Google Apps Engine:

The Python Runtime Environment

The Python Runtime Environment that uses Python version 2.5.2. and provides access to Python APIs for the datastore, Google Accounts, URL fetch and email services.  It also includes the Python webapp framework and the Django web application framework, version 0.96.1.  The codes can only be written in Python.  Also, The runtime environment does not support all the modules and components of Python and the webapp framework.

BigTable

The Apps Engine includes BigTable for database operations.  BigTable is used by Google itself for managing structured data for several projects.  BigTable provides a flexible solution and scalable solution for serving database requests of varying sizes while reducing the latency in back-end processing as well as real time front-end data serving.

The DataStore

Built on Google File System (GFS) and accesible through the DataStore API, the DataStore service provides a powerful distributed data storage system which includes a query engine and transactions for powering large distributed data-intensive applications.

The Sandbox

The Sandbox acts both as a “Gateway” as well as a “Gatekeeper” for requests from and responses to the applications in the distributed environment.  The Sandbox can execute code, store and query data, use the App Engine mail, URL fetch and Google Account services, and examine the user’s web request and prepare the response.

Google Accounts, Email and URL Fetch

The applications hosted on the Apps Engine can integrate with the Google accounts to allow users to sign into the application using their Google account information.  The App Engine applications can send email messages using the Mail API and can also communicate with other web services over the Internet using HTTP/HTTPS requests through the URL Fetch service.

The Administration Console

The Google App Engine admin console lets you:

• create a new application, and set up a free appspot.com sub-domain, or a top-level domain name of your choosing
• invite other people to be developers for your application, so they can access the Console and upload new versions of the code
• view access data and error logs, and analyze traffic
• browse your application’s datastore and manage indexes
• test new versions of your application, and switch the version that your users see

Is it really FREE and what are the limitations

Yes, to an extent, the Google App Engine is free.  Every App Engine application is provided 500 MB of storage and bandwidth to cover 5 million monthly page views free of cost.  Some of the limitations, however, can make it a costly affair at this point in time.

Some limitations:

• Support for Python exclusively as the development language for the web apps to be hosted on the Apps Engine.  This can result in higher cost of development for the companies who otherwise do not have Python developers on board.
• An application hosted on the Apps Engine cannot use other services for storage or database operations unlike Amazon which provides flexibility in choosing particular services from it suite of cloud computing offerings.  With Amazon, you can write in any language, pick up any service and integrate your application with the same.
• Only 10,000 developer accounts in the beta release which is already full to capacity.
• No, the applications hosted on the Apps Engine are not limited to Google account holders only as quoted by several blogs including Mashable.

Some useful links:

Google App Engine Home page

Google App Engine Documentation

Google App Engine SDK download

Appspot: Gallery of Google App Engine Applications

Google App Engine FAQ

App Engine Discussion Groups